The present invention derives from the development of a biotechnological fermentation process that produces a yeast sterol mixture enriched in cholesta-5,7,24-triene-3.beta.-ol and accompanied by other di-olefinic yeast sterol metabolites. The aforementioned trienol, having the chemical structure (I), ##STR1## is a valuable compound useful, inter alia, as an intermediate in the synthesis of a variety of compounds related to vitamin D.sub.3 derivatives, e.g., cholesta-5,7-diene-3.beta.-25-diol and other 25-substituted vitamin D.sub.3 precursors. Accordingly, it is necessary to provide a feasible process for isolating and purifying the trienol (I) from a fermentation mixture containing yeast sterol metabolites, including lanosterol, 4,4-dimethylzymosterol, 4-methylzymosterol, zymosterol and cholesta-7,24-diene-3.beta.-ol. The mixture may also include squalene. As may be seen from the following structures, a number of these compounds containing two or more degrees of unsaturation. Thus, the process of isolation and separation must be specific. ##STR2##
S.C. Eyley et al., J. C. S. Perkins Trans. I, pp. 731-735 (1976), describe a method for synthesizing 25-hydroxyprovitamin D.sub.3 and 25.xi.,26-dihydroxyprovitamin D.sub.3. The method involves initial reaction of the C-22 aldehyde derived by degradation of ergosterol with a Grignard reagent derived from 4-chloro-2-methylbut-1-ene, followed by reductive elimination of the mesylate of the resulting C-22 alcohol.
J. P. Moreau et al., J. Org. Chem. 39(14):2018-2023 (1974), is a background reference which describes the synthesis of 5.alpha.-cholesta-7,24-dien-3.beta.-ol and cholesta-5,7,24-trien-3.beta.-ol.
J. W. Blunt et al., Biochemistry 8(2):671-675 (February 1969), describe methods of synthesizing cholesta-5,7-diene-3.beta.,25-diol, followed by conversion to 25-hydroxycholecaliferol.
S. S. Yang et al., Tetrahedron Letters 27:2315-2316 (1977), is a background reference describing a method for synthesizing 25-fluorovitamin D.sub.3.
D. R. Crump et al., J. C. S. Perkins Trans. I, pp. 2731-2733 (1973), describes a method for synthesizing (22S)-hydroxyvitamin D.sub.4 using ergosterol acetate as a starting material. The synthesis involves selective epoxidation of the 22,23-double bond of ergosterol acetate, followed by a Grignard reaction on the hexanor-22-aldehyde, and irradiation.